1. Field of the Invention The invention relates, in general, to printing machines and, in particular, to a new and useful inking device for a printing press, comprising at least one stereo cylinder bearing a printing block, one inking roller with an elastic surface which can be joined to the stereo cylinder, an inking device, which inks up the inking roller and a dosing device which can be joined to the inking roller. A similar arrangement is known from the German Publication No. 32 25 982. Here the ink is transferred from an inkwell onto the inking roller covered by an elastic surface, the inkwell being, defined by a wall holding back the ink on the one side, and by a dosing member on the other side. The dosing member, being joined virtually tangential to the inking roller produces on the inking roller a thin ink layer suitable for the transfer onto the stereo cylinder. Hence, it holds back the ink in the inkwell except for the quantity guided through the slot between dosing member and inking roller. Since the quantity of ink carried off is very small, the ink supply lasts very long in the inkwell.
By reason of the relatively large resting or supporting surface of the dosing member, a huge hydrodynamic pressure is built up in the ink slot. In order to obtain a sufficiently thin and constant ink layer, the dosing member has to be pushed with a large a mount of power against the elastic surface of the inking roller. This high power (engagement power) causes a high strain of the elements taking part in the dosing process, which entails a high wear of these elements. It has to be noted that along with an increasing strain of these elements, an extreme heating up, especially of the ink, is caused. The ink heats up particularly in the region of the edge of the dosing member, since the ink supply is carried off from the dosing slot very slowly. This rise of temperature can be followed by a change of the property of the ink, which affects the printing quality immediately. Cooling devices of correspondingly huge dimensions are supposed to keep the heating under control.
As a consequence of the pushing pressure acting on the dosing member, necessary for the hydrodynamic pressure of the ink in the dosing slot, and, as a consequence of the virtually tangential joining of the dosing member to the inking roller, there is an additional danger that the front edge of the dosing member can be torn into the inking roller by reason of the elastic fashioning of the surface of the inking roller. This is especially likely to happen when there is a lack of ink, and can cause very severe damage to the entire printing press.
The turbulence occurring in the inkwells which is intended to keep the edge of the dosing member free from dirt substances certainly causes disturbances in the ink layers has to provide a high evenness. This turbulence, however, does not exclude reliably all pollution of the edge of the dosing member. However, the dirt substances clinging to the edge of the dosing member have the effect that the ink layer on the inking roller shows stripes, which are transferred onto the plate cylinder in spite of the ink supply swing rollers and thus can be seen on the printed copy. If no measures are taken these dirt substances remain clinging on the edge of the dosing member and influence the printing quality negatively, until the dosing member is cleaned.
Other attempts to produce an ink layer on an inking roller having an elastic surface by means of a single dosing element, such as with the ink layer providing all the necessary conditions for the transfer onto the stereo cylinder, have failed substantially because of the pollution problems which occur. For this reason, none of the solutions suggested so far could be accepted in general.